Polymer electrolyte fuel cell

ABSTRACT

Disclosed is a polymer electrolyte fuel cell including improved separators that cause no mixing of a fuel gas and an oxidant gas. The polymer electrolyte fuel cell comprises a plurality of membrane electrode assemblies and a plurality of conductive separators, wherein the plurality of conductive separators comprise at least one separator comprising: a fuel gas inlet-side manifold aperture; a fuel gas outlet-side manifold aperture; a gas flow channel for fuel gas formed on an anode-side of the separator; an inlet-side through hole and an outlet-side through hole penetrating the separator which are formed at an inlet-side end and an outlet-side end of the gas flow channel for fuel gas; and an inlet-side connection groove and an outlet-side connection groove for connecting the inlet-side and outlet-side through holes with the fuel gas inlet-side manifold aperture and the fuel gas outlet-side manifold aperture, respectively, which are formed on a cathode-side of the separator.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a fuel cell comprising a solidpolymer electrolyte used for portable power sources, electric vehiclepower sources, domestic cogeneration systems, etc.

[0002] A fuel cell comprising a solid polymer electrolyte generateselectric power and heat simultaneously by electrochemically reacting afuel gas containing hydrogen and an oxidant gas containing oxygen suchas air. This fuel cell is basically composed of a polymer electrolytemembrane for selectively transporting hydrogen ions, and a pair ofelectrodes formed on both surfaces of the polymer electrolyte membrane.The electrode usually comprises a catalyst layer which is composedmainly of carbon particles carrying a platinum group metal catalyst anda diffusion layer which has both gas permeability and electronicconductivity and is formed on the outer surface of the catalyst layer.

[0003] Moreover, gaskets or gas sealing materials are arranged on theouter periphery of the electrodes with the polymer electrolyte membranetherebetween so as to prevent a fuel gas and an oxidant gas from leakingout or prevent these two kinds of gases from mixing together. Thegaskets are combined integrally with the electrodes and polymerelectrolyte membrane beforehand. This is called “MEA” (membraneelectrode assembly). Disposed outside the MEA are conductive separatorsfor mechanically securing the MEA and for connecting adjacent MEAselectrically in series. The separators have a gas flow channel forsupplying a reaction gas to the electrode surface and for removing agenerated gas and an excess gas at a portion to come in contact with theMEA. Although the gas flow channel may be provided separately from theseparators, grooves are usually formed on the surfaces of the separatorsto serve as the gas flow channel.

[0004] In order to supply the gas to such grooves, it is necessary touse a piping jig, called “manifold”, which branches out, depending onthe number of the separators, into the grooves of the respectiveseparators from a gas supply pipe. This type of manifold, directlyconnecting the gas supply pipe to the grooves of the separators, isspecifically called “external manifold”. There is also another type ofmanifold, called “Internal manifold”, which has a more simple structure.In the internal manifold, the separators with the gas flow channelformed thereon are provided with through holes, called “manifoldaperture”, which are connected to the inlet and outlet of the gas flowchannel, and the gas is supplied directly from the manifold apertures.

[0005] Since the fuel cell generates heat during operation, it needscooling with cooling water or the like to keep good temperatureconditions. Thus, a cooling section for flowing the cooling watertherein is generally inserted between the separators for every one tothree cells, and the cooling section is often formed by providing thebackside of the separator with a cooling water flow channel. In ageneral structure of the fuel cell, the MEAs, separators and coolingsections, as described above, are alternately stacked to form a stack of10 to 200 cells, and the resultant cell stack is sandwiched by endplates with a current collector plate and an insulating plate interposedbetween the cell stack and each end plate and is clamped with clampingbolts from both sides.

[0006] In such a polymer electrolyte fuel cell, the separators need tohave a high conductivity, high gas tightness, and high corrosionresistance to oxidation/reduction reactions of hydrogen/oxygen. For suchreasons, conventional separators are usually formed from carbonmaterials such as graphite and expanded graphite, and the gas flowchannel is formed by cutting the surface of the separator or by moldingin the case of expanded graphite separator.

[0007] The fuel cell produced in the above-described manner is suppliedwith the fuel gas, oxidant gas and cooling water to examine theperformance of the fuel cell or of a unit cell of the fuel cell.

[0008] The prior art fuel cell, comprising the cell stack in which theMEA is disposed between two conventional conductive separators, poses alarge problem resulting from the separators. Specifically, in such afuel cell, the gasket arranged on the periphery of the MEA is pressed tofall into the gas flow channel of one of the two separators due to theclamping pressure of the fuel cell, thereby to form a clearance betweenthe gasket of the MEA and the other separator. Such a clearance isliable to occur at the ends of the gas flow channel in the vicinity ofthe manifold apertures. Through the clearance, two kinds of gases mixwith each other, resulting in deterioration of cell performance. Also,the mixing of the gasses may cause explosion or firing, thus invitingdangerous situations.

BRIEF SUMMARY OF THE INVENTION

[0009] In view of the above problem of the prior art fuel cell, anobject of the present invention is to provide a polymer electrolyte fuelcell free from mixing of two kinds of gases by improving separators.

[0010] Another object of the invention is to provide an improvedseparator that causes no mixing of two kinds of gasses.

[0011] The present invention is characterized in that in a conductiveseparator, the position at which the end of a gas flow channel isconnected with a manifold aperture is changed in order to prevent mixingof the gases. Therefore, even if a gasket is pressed down toward the gasflow channel of the separator to form a clearance in the contactingportion of the gasket of an MEA and the separator in the vicinity of themanifold aperture in which a gas flows, the same kind of gas as the gasof the manifold aperture flows through the clearance, so that the mixingof the two kinds of gases does not occur in the present invention.

[0012] The present invention provides a polymer electrolyte fuel cellcomprising:

[0013] a fuel cell stack comprising a plurality of conductive separatorsand a plurality of membrane electrode assemblies that are stacked withone of the conductive separators interposed therebetween, each of themembrane electrode assemblies comprising a polymer electrolyte membrane,and an anode and a cathode sandwiching the polymer electrolyte membrane;

[0014] a means for supplying a fuel gas to the anode; and

[0015] a means for supplying an oxidant gas to the cathode,

[0016] wherein the plurality of conductive separators comprise at leastone separator comprising: a fuel gas inlet-side manifold aperture; afuel gas outlet-side manifold aperture; a gas flow channel for supplyingthe fuel gas to the anode which is formed on an anode-side of theseparator; an inlet-side through hole and an outlet-side through holepenetrating the separator which are formed at an inlet-side end and anoutlet-side end of the gas flow channel for fuel gas; and an inlet-sideconnection groove and an outlet-side connection groove for connectingthe inlet-side and outlet-side through holes with the fuel gasinlet-side manifold aperture and the fuel gas outlet-side manifoldaperture, respectively, which are formed on a cathode-side of theseparator.

[0017] It is preferable that the membrane electrode assembly furthercomprises a gasket covering an outer periphery of the anode and thecathode and that the gasket comprises a fuel gas inlet-side manifoldaperture and a fuel gas outlet-side manifold aperture.

[0018] While the novel features of the invention are set forthparticularly in the appended claims, the invention, both as toorganization and content, will be better understood and appreciated,along with other objects and features thereof, from the followingdetailed description taken in conjunction with the drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

[0019]FIG. 1 is a front view illustrating a membrane electrode assemblyof a fuel cell in one embodiment of the present invention.

[0020]FIG. 2 is a front view illustrating a cathode-side of a conductiveseparator of a fuel cell in Embodiment 1 of the present invention.

[0021]FIG. 3 is a front view illustrating an anode-side of theconductive separator as shown in FIG. 2.

[0022]FIG. 4 is a front view illustrating a cathode-side of acathode-side conductive separator member of the fuel cell in Embodiment1 of the present invention.

[0023]FIG. 5 is a front view illustrating the backside of thecathode-side conductive separator member as shown in FIG. 4.

[0024]FIG. 6 is a front view illustrating the backside of an anode-sideconductive separator member of the fuel cell in Embodiment 1 of thepresent invention.

[0025]FIG. 7 is a front view illustrating an anode-side of theanode-side conductive separator member as shown in FIG. 6.

[0026]FIG. 8 is a cross-sectional view of the vital part of a cell stackof the fuel cell in Embodiment 1 of the present invention.

[0027]FIG. 9 is a front view illustrating a cathode-side of acathode-side conductive separator member of a fuel cell in Embodiment 2of the present invention.

[0028]FIG. 10 is a front view illustrating the backside of thecathode-side conductive separator member as shown in FIG. 9.

[0029]FIG. 11 is a front view illustrating the backside of an anode-sideconductive separator member of the fuel cell in Embodiment 2 of thepresent invention.

[0030]FIG. 12 is a front view illustrating an anode-side of theanode-side conductive separator member as shown in FIG. 11.

[0031]FIG. 13 is a cross-sectional view of the vital part of a cellstack of the fuel cell in Embodiment 2 of the present invention.

[0032]FIG. 14 is a cross-sectional view of the vital part of a cellstack of a prior art fuel cell comprising conventional separators.

DETAILED DESCRIPTION OF THE INVENTION

[0033] The present invention provides a polymer electrolyte fuel cellcomprising a plurality of conductive separators and a plurality ofmembrane electrode assemblies, wherein the plurality of conductiveseparators comprise at least one separator comprising: a fuel gasinlet-side manifold aperture; a fuel gas outlet-side manifold aperture:a gas flow channel for supplying the fuel gas to the anode which isformed on an anode-side of the separator; an inlet-side through hole andan outlet-side through hole penetrating the separator which are formedat an inlet-side end and an outlet-side end of the gas flow channel forfuel gas; and an inlet-side connection groove and an outlet-sideconnection groove for connecting the inlet-side and outlet-side throughholes with the fuel gas inlet-side manifold aperture and the fuel gasoutlet-side manifold aperture, respectively, which are formed on acathode-side of the separator.

[0034] In a preferred mode of the conductive separator, the at least oneseparator further comprises: an oxidant gas inlet-side manifoldaperture; an oxidant gas outlet-side manifold aperture; a gas flowchannel for supplying the oxidant gas to the cathode which is formed onthe cathode-side; an inlet-side through hole and an outlet-side throughhole penetrating the separator which are formed at an inlet-side end andan outlet-side end of the gas flow channel for oxidant gas; and aninlet-side connection groove and an outlet-side connection groove forconnecting the inlet-side and outlet-side through holes with the oxidantgas inlet-side manifold aperture and the oxidant gas outlet-sidemanifold aperture, respectively, which are formed on the anode-side.

[0035] In another preferred mode of the conductive separator, the atleast one separator further comprises a cooling water inlet-sidemanifold aperture and a cooling water outlet-side manifold aperture, theplurality of conductive separators comprise a combination of twoseparator members consisting of an anode-side separator member and acathode-side separator member, each separator member comprising at leasta fuel gas inlet-side manifold aperture, a fuel gas outlet-side manifoldaperture, a cooling water inlet-side manifold aperture, and a coolingwater outlet-side manifold aperture, the two separator members beingcombined in such a manner that their backsides are in contact with eachother,

[0036] the anode-side separator member further comprises: a gas flowchannel for supplying the fuel gas to the anode which is formed on ananode-side of the anode-side separator member; an inlet-side throughhole and an outlet-side through hole penetrating the anode-sideseparator member which are formed at an inlet-side end and anoutlet-side end of the gas flow channel; and an inlet-side connectiongroove and an outlet-side connection groove for connecting theinlet-side and outlet-side through holes with the fuel gas inlet-sidemanifold aperture and the fuel gas outlet-side manifold aperture,respectively, which are formed on the backside of the anode-sideseparator member,

[0037] at least one of the two separator members has, on the backsidethereof, a cooling water flow channel communicating with the coolingwater inlet-side manifold aperture and the cooling water outlet-sidemanifold aperture such that the cooling water flow channel is formedbetween the two separator members, and

[0038] the respective manifold apertures of the at least one separatorcommunicate with the corresponding manifold apertures of each of the twoseparator members.

[0039] In still another preferred mode of the conductive separator, theat least one separator further comprises an oxidant gas inlet-sidemanifold aperture and an oxidant gas outlet-side manifold aperture,

[0040] the two separator members further comprise an oxidant gasinlet-side manifold aperture and an oxidant gas outlet-side manifoldaperture,

[0041] the cathode-side separator member further comprises: a gas flowchannel for supplying the oxidant gas to the cathode which is formed ona cathode-side of the cathode-side separator member; an inlet-sidethrough hole and an outlet-side through hole penetrating thecathode-side separator member which are formed at an inlet-side end andan outlet-side end of the gas flow channel; and an inlet-side connectiongroove and an outlet-side connection groove for connecting theinlet-side and outlet-side through holes with the oxidant gas inlet-sidemanifold aperture and the oxidant gas outlet-side manifold aperture,respectively, which are formed on the backside of the cathode-sideseparator member, and

[0042] the respective oxidant gas manifold apertures of the at least oneseparator communicate with the corresponding oxidant gas manifoldapertures of each of the two separator members.

[0043] In another preferred mode of the conductive separator, the atleast one separator further comprises a cooling water inlet-sidemanifold aperture and a cooling water outlet-side manifold aperture,

[0044] the plurality of conductive separators comprise a combination oftwo separator members consisting of an anode-side separator member and acathode-side separator member, each separator member comprising at leasta fuel gas inlet-side manifold aperture, a fuel gas outlet-side manifoldaperture, a cooling water inlet-side manifold aperture, and a coolingwater outlet-side manifold aperture, the two separator members beingcombined in such a manner that their backsides are in contact with eachother,

[0045] the anode-side separator member further comprises: a gas flowchannel for supplying the fuel gas to the anode which is formed on ananode-side of the anode-side separator member; and an inlet-side throughhole and an outlet-side through hole for fuel gas penetrating theanode-side separator member which are formed at an inlet-side end and anoutlet-side end of the gas flow channel,

[0046] the cathode-side separator member further comprises: aninlet-side through hole and an outlet-side through hole for fuel gascommunicating with the inlet-side and outlet-side through holes for fuelgas of the anode-side separator member; and an inlet-side connectiongroove and an outlet-side connection groove for connecting theinlet-side and outlet-side through holes for fuel gas of thecathode-side separator member with the fuel gas inlet-side manifoldaperture and the fuel gas outlet-side manifold aperture, respectively,which are formed on a cathode-side of the cathode-side separator member,

[0047] at least one of the two separator members has, on the backsidethereof, a cooling water flow channel communicating with the coolingwater inlet-side manifold aperture and the cooling water outlet-sidemanifold aperture such that the cooling water flow channel is formedbetween the two separator members, and

[0048] the respective manifold apertures of the at least one separatorcommunicate with the corresponding manifold apertures of each of the twoseparator members.

[0049] In still another preferred mode of the conductive separator, theat least one separator further comprises an oxidant gas inlet-sidemanifold aperture and an oxidant gas outlet-side manifold aperture,

[0050] the two separator members further comprise an oxidant gasinlet-side manifold aperture and an oxidant gas outlet-side manifoldaperture,

[0051] the cathode-side separator member further comprises: a gas flowchannel for supplying the oxidant gas to the cathode which is formed onthe cathode-side; and an inlet-side through hole and an outlet-sidethrough hole for oxidant gas penetrating the cathode-side separatormember which are formed at an inlet-side end and an outlet-side end ofthe gas flow channel,

[0052] the anode-side separator member further comprises: an inlet-sidethrough hole and an outlet-side through hole for oxidant gascommunicating with the inlet-side and outlet-side through holes foroxidant gas of the cathode-side separator member; and an inlet-sideconnection groove and an outlet-side connection groove for connectingthe inlet-side and outlet-side through holes for oxidant gas of theanode-side separator member with the oxidant gas inlet-side manifoldaperture and the oxidant gas outlet-side manifold aperture,respectively, which are formed on the anode-side, and

[0053] the respective oxidant gas manifold apertures of the at least oneseparator communicate with the corresponding oxidant gas manifoldapertures of each of the two separator members.

[0054] It is preferable that the membrane electrode assembly furthercomprises a gasket covering an outer periphery of the anode and thecathode, and that the gasket comprises a fuel gas inlet-side manifoldaperture, a fuel gas outlet-side manifold aperture, an oxidant gasinlet-side manifold aperture, an oxidant gas outlet-side manifoldaperture, a cooling water inlet-side manifold aperture, and a coolingwater outlet-side manifold aperture, the respective manifold aperturesof the gasket communicating with the corresponding manifold apertures ofeach of the two separator members.

[0055] In the following, embodiments of the present invention will bedescribed with reference to drawings.

[0056] Embodiment 1

[0057]FIG. 1 is a front view illustrating a membrane electrode assembly(hereinafter referred to as MEA). An MEA 6 comprises a polymerelectrolyte membrane, a cathode and an anode sandwiching the electrolytemembrane, and a gasket that is bonded to the periphery of the cathodeand anode so as to cover exposed portions of the electrolyte membrane.In FIG. 1, numeral 4 represents an electrode portion, specifically ananode in this case (the backside of the electrode portion 4 is acathode), and numeral 5 is a gasket portion.

[0058]FIGS. 2 and 3 illustrate a conductive separator in accordance withone embodiment of the present invention.

[0059] A separator 10 has, on the periphery corresponding to the gasketportion 5 of the MEA 6, an oxidant gas inlet-side manifold aperture 11a, an oxidant gas outlet-side manifold aperture 11 b, a fuel gasinlet-side manifold aperture 12 a, a fuel gas outlet-side manifoldaperture 12 b, a cooling water inlet-side manifold aperture 13 a, and acooling water outlet-side manifold aperture 13 b.

[0060] The separator 10 also has, on a cathode-side, a plurality of gasflow channels 14 which are linear and parallel to each other forsupplying an oxidant gas to a cathode and has, on an anode-side, aplurality of parallel gas flow channels 24 for supplying a fuel gas toan anode. The gas flow channels 24 have a serpentine shape that is acombination of straight lines and turns. In FIGS. 2 and 3, the portioninside the dashed line and the portion outside the dashed line are tocome in contact with the electrode portion 4 and the gasket portion 5 ofthe MEA 6, respectively.

[0061] The ends of the gas flow channels 14 for oxidant gas are locatedat portions of the separator 10 to come in contact with the gasketportion 5 and have through holes 15 a and 15 b. In order to connect thethrough holes 15 a and 15 b with the inlet-side manifold aperture 11 aand the outlet-side manifold aperture 11 b, respectively, connectiongrooves 16 a and 16 b are provided on the other side of the separator10, i.e., on the anode-side of the separator 10.

[0062] Similarly, the ends of the gas flow channels 24 for fuel gas arelocated at portions of the separator 10 to come in contact with thegasket portion 5 and have through holes 25 a and 25 b. In order toconnect the through holes 25 a and 25 b with the inlet-side manifoldaperture 12 a and the outlet-side manifold aperture 12 b, respectively,connection grooves 26 a and 26 b are provided on the cathode-side of theseparator.

[0063]FIG. 8 is a cross-sectional view of the vital part of a cell stackin which the MEAs are stacked with the separator 10 interposedtherebetween.

[0064] The oxidant gas supplied to the inlet-side manifold aperture 11 apasses through the connection grooves 16 a formed on the anode-side ofthe separator 10 and the through holes 15 a penetrating the separator 10and reaches the gas flow channels 14 formed on the cathode-side to besupplied to the cathode. An excessive gas and a gas generated by theelectrode reaction pass from the gas flow channels 14 through thethrough holes 15 b penetrating the separator 10 and the connectiongrooves 16 b formed on the anode-side and reach the outlet-side manifoldaperture 11 b to be discharged.

[0065] The fuel gas supplied to the inlet-side manifold aperture 12 apasses through the connection grooves 26 a formed on the cathode-side ofthe separator 10 and the through holes 25 a penetrating the separator 10and reaches the gas flow channels 24 formed on the anode-side to besupplied to the anode. An excessive gas and a gas generated by theelectrode reaction pass from the gas flow channels 24 through thethrough holes 25 b penetrating the separator 10 and the connectiongrooves 26 b formed on the cathode-side and reach the outlet-sidemanifold aperture 12 b to be discharged.

[0066]FIGS. 4 and 5 illustrate a cathode-side conductive separatormember having cooling water flow channels formed on the backsidethereof, and FIGS. 6 and 7 illustrate an anode-side conductive separatormember having cooling water flow channels formed on the backsidethereof.

[0067] A cathode-side conductive separator member 40 has an oxidant gasinlet-side manifold aperture 41 a, an oxidant gas outlet-side manifoldaperture 41 b, a fuel gas inlet-side manifold aperture 42 a, a fuel gasoutlet-side manifold aperture 42 b, a cooling water inlet-side manifoldaperture 43 a, and a cooling water outlet-side manifold aperture 43 b.

[0068] The separator member 40 also has, on a cathode-side thereof, aplurality of gas flow channels 44 for oxidant gas, and has through holes45 a and 45 b formed at the ends of the gas flow channels 44. In orderto connect the through holes 45 a and 45 b with the inlet-side manifoldaperture 41 a and the outlet-side manifold aperture 41 b, respectively,connection grooves 46 a and 46 b are provided on the backside of theseparator member 40.

[0069] The structure of the separator member 40 is the same as that ofthe separator 10 except that the separator member 40 has cooling waterflow channels 47, of which ends directly communicate with the inlet-sidemanifold aperture 43 a and the outlet-side manifold aperture 43 b,instead of the gas flow channels for fuel gas.

[0070] An anode-side conductive separator member 50 has an oxidant gasinlet-side manifold aperture 51 a, an oxidant gas outlet-side manifoldaperture 51 b, a fuel gas inlet-side manifold aperture 52 a, a fuel gasoutlet-side manifold aperture 52 b, a cooling water inlet-side manifoldaperture 53 a, and a cooling water outlet-side manifold aperture 53 b.

[0071] The anode-side conductive separator member 50 has, on an anodeside thereof, a plurality of gas flow channels 54 for fuel gas, and hasthrough holes 55 a and 55 b formed at the ends of the gas flow channels54. In order to connect the through holes 55 a and 55 b with theinlet-side manifold aperture 52 a and the outlet-side manifold aperture52 b, respectively, connection grooves 56 a and 56 b are provided on thebackside of the separator member 50.

[0072] The separator member 50 also has, on the backside thereof,cooling water flow channels 57, of which ends directly communicate withthe inlet-side manifold aperture 53 a and the outlet-side manifoldaperture 53 b.

[0073] The cathode-side separator member 40 and the anode-side separatormember 50, combined to each other with their backsides having thecooling water flow channels 47 and 57 in contact with each other, areinserted between the MEAs. FIG. 8 is a cross-sectional view of a cellstack in which the combination of the cathode-side separator member 40and anode-side separator member 50 is alternately inserted with theseparator 10 between the MEAs.

[0074] The oxidant gas supplied to the inlet-side manifold apertures 41a and 51 a passes through the connection grooves 46 a formed on thebackside of the cathode-side separator member 40 and the through holes45 a and reaches the gas flow channels 44 to be supplied to the cathode.An excessive gas and a generated gas pass from the gas flow channels 44through the through holes 45 b and the connection grooves 46 b and reachthe outlet-side manifold aperture 41 b to be discharged.

[0075] Similarly, the fuel gas supplied to the inlet-side manifoldaperture 42 a and 52 a passes through the connection grooves 56 a formedon the backside of the anode-side separator member 50 and the throughholes 55 a and reaches the gas flow channels 54 to be supplied to theanode. An excessive gas and a generated gas pass from the gas flowchannels 54 through the through holes 55 b and the connection grooves 56b and reach the outlet-side manifold aperture 52 b to be discharged.

[0076] The cooling water supplied to the inlet-side manifold apertures43 a and 53 a passes through the serpentine cooling water flow channels47 and 57 and is discharged from the outlet-side manifold apertures 43 band 53 b. In this manner, the cooling water cools fuel cells from thebacksides of the cathode-side separator member 40 and anode-sideseparator member 50.

[0077] For cooling the cells, water is generally and conveniently used,but an antifreezing solution such as ethylene glycol may be used.

[0078]FIG. 14 is a cross-sectional view of the vital part of a cellstack comprising conventional separators 100. The separator 100 has, ona cathode side thereof, a gas flow channel for oxidant gas 104communicating with an oxidant gas manifold aperture 111 and has, on ananode side thereof, a gas flow channel for fuel gas 114 communicatingwith a fuel gas manifold aperture. When the cell stack is clamped in thestacking direction of unit cells, a gasket 5 of an MEA 6 may be pressedto fall into the channel 104 in the vicinity of the manifold aperture111 due to the clamping pressure. In this case, the gasket 5 and anadjoining portion of an electrode portion 4 become deformed toward thechannel 104 as shown by the dotted line of FIG. 14, thereby creating aclearance 7 on the anode side between the deformed electrode portion 4′and gasket 5′ and the adjoining separator 100. In the event that theclearance 7 communicates with the gas flow channel for fuel gas 114, thefuel gas is mixed with the oxidant gas from the manifold aperture 111.

[0079] To the contrary, in the present invention, the gas flow channelfor oxidant gas 14 of the separator 10 communicates with the manifoldaperture 11 a through the through hole 15 a and the connection groove 16a formed on the anode-side, as shown in FIG. 8. Even if the MEA ispressed down into the gas flow channel 14, the gasket 5 of the MEA isreceived by the portion of the separator 10 without any channel orgroove between the through hole 15 a and the manifold aperture 11 a.Thus, the gasket 55 does not fall into the gas flow channel for oxidantgas 14 on the cathode side of the separator 10 in the vicinity of themanifold aperture 11 a, so that such a clearance as to connect the gasflow channel for fuel gas 24 with the oxidant gas manifold aperture 11 ais not created on the anode side between the gasket and the adjoiningseparator. Further, if another gasket falls into the adjoiningconnection groove 16 a communicating with the oxidant gas manifoldaperture 11 a to form a clearance on the cathode side between the gasketand the adjoining separator member 40, the clearance communicates withthe oxidant gas manifold aperture or gas flow channel for oxidant gas,so that no mixing of the oxidant gas with the fuel gas occurs.

[0080] Although the above paragraph described the case of the gasketfalling into the oxidant gas channel, the present invention causes nomixing of the oxidant gas with the fuel gas also in the case of thegasket falling into the fuel gas channel.

[0081] Embodiment 2

[0082] The following will describe another embodiment of thecathode-side and anode-side separator members with cooling water flowchannels.

[0083]FIGS. 9 and 10 illustrate a cathode-side conductive separatormember having cooling water flow channels formed on the backsidethereof, and FIGS. 11 and 12 illustrate an anode-side conductiveseparator member having cooling water flow channels formed on thebackside thereof.

[0084] A cathode-side conductive separator member 60 has an oxidant gasinlet-side manifold aperture 61 a, an oxidant gas outlet-side manifoldaperture 61 b, a fuel gas inlet-side manifold aperture 62 a, a fuel gasoutlet-side manifold aperture 62 b, a cooling water inlet-side manifoldaperture 63 a, and a cooling water outlet-side manifold aperture 63 b.

[0085] The separator member 60 also has, on a cathode side thereof, aplurality of gas flow channels 64 for oxidant gas, and has through holes65 a and 65 b formed at the ends of the gas flow channels 64. Theseparator member 60 further has through holes 95 a and 95 b for fuel gascommunicating with through holes for fuel gas 75 a and 75 b,respectively, of an anode-side separator member 70 that will bedescribed later. In order to connect the through holes 95 a and 95 b forfuel gas with the fuel gas inlet-side manifold aperture 62 a and thefuel gas outlet-side manifold aperture 62 b, respectively, the separatormember 60 still further has connection grooves for fuel gas 96 a and 96b on the cathode-side.

[0086] The separator member 60 has, on the backside thereof, serpentinecooling water flow channels 67, of which inlet-side end and outlet-sideend communicate with the inlet-side manifold aperture 63 a and theoutlet-side manifold aperture 63 b, respectively.

[0087] An anode-side conductive separator member 70 has an oxidant gasinlet-side manifold aperture 71 a, an oxidant gas outlet-side manifoldaperture 71 b, a fuel gas inlet-side manifold aperture 72 a, a fuel gasoutlet-side manifold aperture 72 b, a cooling water inlet-side manifoldaperture 73 a, and a cooling water outlet-side manifold aperture 73 b.

[0088] The anode-side conductive separator member 70 also has, on ananode side thereof, a plurality of gas flow channels 74 for fuel gas,and has through holes for fuel gal 75 a and 75 b formed at the ends ofthe gas flow channels 74. The separator member 70 further has throughholes for oxidant gas 85 a and 85 b communicating with the through holesfor oxidant gas 65 a and 65 b, respectively, of the cathode-sideseparator member 60. In order to connect the through holes for oxidantgas 85 a and 85 b with the oxidant gas inlet-side manifold aperture 71 aand the oxidant gas outlet-side manifold aperture 71 b, respectively,the separator member 70 still further has connection grooves for oxidantgas 86 a and 86 b on the anode side.

[0089] The separator member 70 has, on the backside thereof, serpentinecooling water flow channels 77, of which inlet-side end and outlet-sideend communicate with the inlet-side manifold aperture 73 a and theoutlet-side manifold aperture 73 b, respectively.

[0090] The cathode-side separator member 60 and the anode-side separatormember 70, combined to each other with their backsides having thecooling water flow channels 67 and 77 in contact with each other, areinserted between the MEAS. FIG. 13 is a cross-sectional view of a cellstack in which the combination of the cathode-side separator member 60and anode-side separator member 70 is alternately inserted with theseparator 10 between the MEAs.

[0091] The oxidant gas supplied to the inlet-side manifold apertures 61a and 71 a passes through the connection grooves 86 a formed on theanode-side of the anode-side separator member 70 and the through holes85 a and 65 a and reaches the gas flow channels 64 to be supplied to thecathode. An excessive gas and a generated gas pass from the gas flowchannels 64 through the through holes 65 b and 85 b and the connectiongrooves 86 b and reach the outlet-side manifold aperture 71 b to bedischarged.

[0092] Similarly, the fuel gas supplied to the inlet-side manifoldaperture 62 a of the cathode-side separator member 60 passes through theconnection grooves 96 a and the through holes 95 a and 75 a and reachesthe gas flow channels 74 formed on the anode-side of the anode-sideseparator member 70 to be supplied to the anode. An excessive gas and agenerated gas pass from the gas flow channels 74 through the throughholes 75 b and 95 b and the connection grooves 96 b and reach theoutlet-side manifold aperture 62 b to be discharged.

[0093] The cooling water supplied to the inlet-side manifold apertures63 a and 73 a passes through the serpentine cooling water channels 67and 77 and is discharged from the outlet-side manifold apertures 63 band 73 b. In this manner, the cooling water cools fuel cells from thebacksides of the cathode-side separator member 60 and anode-sideseparator member 70.

[0094] As in the foregoing embodiment, it is clear that a cross leak ofthe fuel gas and the oxidant gas does not occur also in this embodimentusing the combination of the cathode-side separator member 60 andanode-side separator member 70 for forming cooling water flow channels.

[0095] Although the cooling water flow channels were formed on opposingsides of two separator members in the foregoing embodiments, they may beformed only on one separator member.

[0096] As described above, in a fuel cell in which conductive separatorsand MEAs are laminated, the present invention can prevent a cross leakof two different gases from occurring at edges of the contacting portionof the conductive separator and the gasket of the MEA in the vicinity ofa manifold aperture.

[0097] In the above-described embodiments, a plurality of parallel gasflow channels for supplying the oxidant gas or the fuel gas were formed,but just one gas flow channel may be formed. Similarly, this applies tothe number of cooling water flow channel. In the case of one gas flowchannel, the number of inlet-side through hole, outlet-side throughhole, inlet-side connection groove and outlet-side connection groove maybe just one.

[0098] In the embodiments, one gasket covered both sides of theelectrolyte membrane exposed to outside, but two gaskets may be used tocover each side of the electrolyte membrane exposed to outside.

[0099] In the following, examples of the present invention will bedescribed.

EXAMPLE 1

[0100] A conductive carbon powder having an average particle size of 30nm (Ketgenblack EC, manufactured by Akzochimie in Holland) was allowedto carry platinum particles having an average particle size of about 30Å in a weight ratio of 75:25, which gave an electrode catalyst powder. Adispersion of this catalyst powder in isopropanol was mixed with adispersion of perfluorocarbon sulfonic acid powder in ethyl alcoholrepresented by the following chemical formula to prepare a paste. Thispaste was printed on one side of a 250 μm thick carbon fiber nonwovenfabric by screen printing to form an electrode catalyst layer. Theelectrode catalyst layer was formed so as to contain 0.5 mg/cm² platinumand 1.2 mg/cm² perfluorocarbon sulfonic acid. In this manner, by formingthe catalyst layer on the carbon fiber non-woven fabric serving as adiffusion layer, cathodes and anodes having the same structure wereproduced.

[0101] wherein m=1, n=2, x=5 to 13.5, and y≈1000.

[0102] A cathode and an anode thus produced were bonded, by hotpressing, to both sides of the center part of a hydrogen-ion conductivepolymer electrolyte membrane having an area slightly larger than that ofthe electrode in such a manner that each of the printed catalyst layersof the electrodes was in contact with the electrolyte membrane. Thisgave an MEA (membrane electrode assembly). The proton conductive polymerelectrolyte membrane used in this example was a 25 μm thick thin film ofperfluorocarbon sulfonic acid represented by the above-mentionedchemical formula wherein m=2 in this case. The structure of this MEA isshown in FIG. 1, in which numeral 6 represents the MEA, numeral 4 theelectrode portion, and numeral 5 the gasket portion arranged on theouter periphery of the electrode portion 4.

[0103] In this example, a polymer electrolyte fuel cell as shown in FIG.8 was assembled using the separators 10, 40 and 50 as shown in FIGS. 2to 7.

[0104] These separators were produced by processing a plate of isotropicgraphite having a thickness of 2 mm, a height of 130 mm and a width of260 mm with the following specifications. The gas flow channels foroxidant gas 14 and 44 were formed to have a width of about 2 mm and apitch of 2.9 mm in a 20 cm×9 cm area at the center of a cathode-side ofthe graphite plate. Similarly, the gas flow channels for fuel gas 24 and54 were formed to have a serpentine shape with the same width and pitchon an anode-side of the plate. The cooling water flow channels 47 and 57were produced to have a width of about 2 mm and a pitch of 2.9 mm.

[0105] In the separator 10, the cathode-side gas flow channels 14 andanode-side gas flow channels 24 were formed with their center lines ofthe linear part exactly corresponding to each other, in order to preventexcessive shearing force from being applied to the electrodes. Also, thecombination of the separator members 40 and 50 was inserted every twounit cells to provide the polymer electrolyte fuel cell with coolingsections for flowing cooling water therein. For forming the coolingsections, two kinds of the separator members 40 and 50 having coolingwater flow channels were bonded to each other with a sealant (#1211,Liquid Gasket of Solventless Silicon & Sag Type, manufactured by ThreeBond Co., Ltd) in such a manner that their sides having the coolingwater flow channels faced each other. With regard to the gas tightness,the gasket bonded to the MEA was used to air-tightly seal thecombination of the separator and the MEA, while the sealant, #1211, wasused to air-tightly seal the combination of two separator members.

[0106] The MEAs thus produced were stacked with the above-describedseparators interposed therebetween to form a stack of 50 cells, and theresultant cell stack was clamped with current collector plates,insulating plates and stainless steel end plates, using clamping rodswith a pressure of 10 kgf/cm².

[0107] While the resultant polymer electrolyte fuel cell of this examplewas held at 85° C., a hydrogen gas humidified and heated to have a dewpoint of 83° C. was supplied to the anode and air humidified and heatedto have a dew point of 78° C. was supplied to the cathode. Table 1 showsthe results of cell examination. Changes in cell voltage with a currentof 36A, 90A and 126A are shown in Table 1, indicating that the polymerelectrolyte fuel cell of this example is practically effective althoughthe deterioration of the voltage increases with increasing current.TABLE 1 Operating time (hour) Current (A) 10 1000 2000 3000 36 36 V 33 V32 V 31 V 90 34 V 31 V 29 V 27 V 126  31 V 27 V 26 V 25 V

EXAMPLE 2

[0108] In this example, a polymer electrolyte fuel cell was assembled inthe same manner as in Example 1 except for the use of the combination ofthe separator members 60 and 70 for forming cooling water flow channels.While this polymer electrolyte fuel cell was held at 75° C., a hydrogengas humidified and heated to have a dew point of 70° C. was supplied tothe anode and air humidified and heated to have a dew point of 65° C.was supplied to the cathode. The results indicate that the fuel cell ofthis example has almost the same performance as that of Example 1.

[0109] As described above, in a fuel cell in which conductive separatorsand MEAs are laminated, the present invention can prevent a cross leakof two different gases from occurring at edges of the contacting portionof the conductive separator and the gasket of the MEA in the vicinity ofa manifold aperture.

[0110] Although the present invention has been described in terms of thepresently preferred embodiments, it is to be understood that suchdisclosure is not to be interpreted as limiting. Various alterations andmodifications will no doubt become apparent to those skilled in the artto which the present invention pertains, after having read the abovedisclosure. Accordingly, it is intended that the appended claims beinterpreted as covering all alterations and modifications as fall withinthe true spirit and scope of the invention.

1. A polymer electrolyte fuel cell comprising: a fuel cell stackcomprising a plurality of conductive separators and a plurality ofmembrane electrode assemblies that are stacked with one of saidconductive separators interposed therebetween, each of said membraneelectrode assemblies comprising a polymer electrolyte membrane, and ananode and a cathode sandwiching said polymer electrolyte membrane; ameans for supplying a fuel gas to said anode; and a means for supplyingan oxidant gas to said cathode, wherein said plurality of conductiveseparators comprise at least one separator comprising: a fuel gasinlet-side manifold aperture; a fuel gas outlet-side manifold aperture;a gas flow channel for supplying the fuel gas to said anode which isformed on an anode-side of the separator; an inlet-side through hole andan outlet-side through hole penetrating the separator which are formedat an inlet-side end and an outlet-side end of said gas flow channel forfuel gas; and an inlet-side connection groove and an outlet-sideconnection groove for connecting said inlet-side and outlet-side throughholes with said fuel gas inlet-side manifold aperture and said fuel gasoutlet-side manifold aperture, respectively, which are formed on acathode-side of the separator.
 2. The polymer electrolyte fuel cell inaccordance with claim 1, wherein said at least one separator furthercomprises: an oxidant gas inlet-side manifold aperture; an oxidant gasoutlet-side manifold aperture; a gas flow channel for supplying theoxidant gas to said cathode which is formed on said cathode-side; aninlet-side through hole and an outlet-side through hole penetrating theseparator which are formed at an inlet-side end and an outlet-side endof said gas flow channel for oxidant gas; and an inlet-side connectiongroove and an outlet-side connection groove for connecting saidinlet-side and outlet-side through holes with said oxidant gasinlet-side manifold aperture and said oxidant gas outlet-side manifoldaperture, respectively, which are formed on said anode-side.
 3. Thepolymer electrolyte fuel cell in accordance with claim 1, wherein saidat least one separator further comprises a cooling water inlet-sidemanifold aperture and a cooling water outlet-side manifold aperture,said plurality of conductive separators comprise a combination of twoseparator members consisting of an anode-side separator member and acathode-side separator member, each separator member comprising at leasta fuel gas inlet-side manifold aperture, a fuel gas outlet-side manifoldaperture, a cooling water inlet-side manifold aperture, and a coolingwater outlet-side manifold aperture, said two separator members beingcombined in such a manner that their backsides are in contact with eachother, said anode-side separator member further comprises: a gas flowchannel for supplying the fuel gas to said anode which is formed on ananode-side of the anode-side separator member; an inlet-side throughhole and an outlet-side through hole penetrating the anode-sideseparator member which are formed at an inlet-side end and anoutlet-side end of said gas flow channel; and an inlet-side connectiongroove and an outlet-side connection groove for connecting saidinlet-side and outlet-side through holes with said fuel gas inlet-sidemanifold aperture and said fuel gas outlet-side manifold aperture,respectively, which are formed on the backside of the anode-sideseparator member, at least one of said two separator members has, on thebackside thereof, a cooling water flow channel communicating with saidcooling water inlet-side manifold aperture and said cooling wateroutlet-side manifold aperture such that the cooling water flow channelis formed between said two separator members, and said respectivemanifold apertures of said at least one separator communicate with saidcorresponding manifold apertures of each of said two separator members.4. The polymer electrolyte fuel cell in accordance with claim 3, whereinsaid at least one separator further comprises an oxidant gas inlet-sidemanifold aperture and an oxidant gas outlet-side manifold aperture, saidtwo separator members further comprise an oxidant gas inlet-sidemanifold aperture and an oxidant gas outlet-side manifold aperture, saidcathode-side separator member further comprises: a gas flow channel forsupplying the oxidant gas to said cathode which is formed on acathode-side of the cathode-side separator member; an inlet-side throughhole and an outlet-side through hole penetrating the cathode-sideseparator member which are formed at an inlet-side end and anoutlet-side end of said gas flow channel; and an inlet-side connectiongroove and an outlet-side connection groove for connecting saidinlet-side and outlet-side through holes with said oxidant gasinlet-side manifold aperture and said oxidant gas outlet-side manifoldaperture, respectively, which are formed on the backside of thecathode-side separator member, and said respective oxidant gas manifoldapertures of said at least one separator communicate with saidcorresponding oxidant gas manifold apertures of each of said twoseparator members.
 5. The polymer electrolyte fuel cell in accordancewith claim 1, wherein said at least one separator further comprises acooling water inlet-side manifold aperture and a cooling wateroutlet-side manifold aperture, said plurality of conductive separatorscomprise a combination of two separator members consisting of ananode-side separator member and a cathode-side separator member, eachseparator member comprising at least a fuel gas inlet-side manifoldaperture, a fuel gas outlet-side manifold aperture, a cooling waterinlet-side manifold aperture, and a cooling water outlet-side manifoldaperture, said two separator members being combined in such a mannerthat their backsides are in contact with each other, said anode-sideseparator member further comprises: a gas flow channel for supplying thefuel gas to said anode which is formed on an anode-side of theanode-side separator member; and an inlet-side through hole and anoutlet-side through hole for fuel gas penetrating the anode-sideseparator member which are formed at an inlet-side end and anoutlet-side end of said gas flow channel, said cathode-side separatormember further comprises: an inlet-side through hole and an outlet-sidethrough hole for fuel gas communicating with said inlet-side andoutlet-side through holes for fuel gas of said anode-side separatormember; and an inlet-side connection groove and an outlet-sideconnection groove for connecting said inlet-side and outlet-side throughholes for fuel gas of said cathode-side separator member with said fuelgas inlet-side manifold aperture and said fuel gas outlet-side manifoldaperture, respectively, which are formed on a cathode-side of thecathode-side separator member, at least one of said two separatormembers has, on the backside thereof, a cooling water flow channelcommunicating with said cooling water inlet-side manifold aperture andsaid cooling water outlet-side manifold aperture such that the coolingwater flow channel is formed between said two separator members, andsaid respective manifold apertures of said at least one separatorcommunicate with said corresponding manifold apertures of each of saidtwo separator members.
 6. The polymer electrolyte fuel cell inaccordance with claim 5, wherein said at least one separator furthercomprises an oxidant gas inlet-side manifold aperture and an oxidant gasoutlet-side manifold aperture, said two separator members furthercomprise an oxidant gas inlet-side manifold aperture and an oxidant gasoutlet-side manifold aperture, said cathode-side separator memberfurther comprises: a gas flow channel for supplying the oxidant gas tosaid cathode which is formed on said cathode-side; and an inlet-sidethrough hole and an outlet-side through hole for oxidant gas penetratingthe cathode-side separator member which are formed at an inlet-side endand an outlet-side end of said gas flow channel, said anode-sideseparator member further comprises: an inlet-side through hole and anoutlet-side through hole for oxidant gas communicating with saidinlet-side and outlet-side through holes for oxidant gas of saidcathode-side separator member; and an inlet-side connection groove andan outlet-side connection groove for connecting said inlet-side andoutlet-side through holes for oxidant gas of said anode-side separatormember with said oxidant gas inlet-side manifold aperture and saidoxidant gas outlet-side manifold aperture, respectively, which areformed on said anode-side, and said respective oxidant gas manifoldapertures of said at least one separator communicate with saidcorresponding oxidant gas manifold apertures of each of said twoseparator members.
 7. The polymer electrolyte fuel cell in accordancewith claim 4, wherein said membrane electrode assembly further comprisesa gasket covering an outer periphery of said anode and said cathode, andsaid gasket comprises a fuel gas inlet-side manifold aperture, a fuelgas outlet-side manifold aperture, an oxidant gas inlet-side manifoldaperture, an oxidant gas outlet-side manifold aperture, a cooling waterinlet-side manifold aperture, and a cooling water outlet-side manifoldaperture, said respective manifold apertures of said gasketcommunicating with said corresponding manifold apertures of each of saidtwo separator members.
 8. The polymer electrolyte fuel cell inaccordance with claim 6, wherein said membrane electrode assemblyfurther comprises a gasket covering an outer periphery of said anode andsaid cathode, and said gasket comprises a fuel gas inlet-side manifoldaperture, a fuel gas outlet-side manifold aperture, an oxidant gasinlet-side manifold aperture, an oxidant gas outlet-side manifoldaperture, a cooling water inlet-side manifold aperture, and a coolingwater outlet-side manifold aperture, said respective manifold aperturesof said gasket communicating with said corresponding manifold aperturesof each of said two separator members.
 9. A conductive separator for apolymer electrolyte fuel cell, comprising: a fuel gas inlet-sidemanifold aperture; a fuel gas outlet-side manifold aperture; an oxidantgas inlet-side manifold aperture; an oxidant gas outlet-side manifoldaperture; a gas flow channel for fuel gas formed on an anode-side of theseparator; a gas flow channel for oxidant gas formed on a cathode-sideof the separator; an inlet-side through hole and an outlet-side throughhole for fuel gas penetrating the separator which are formed at aninlet-side end and an outlet-side end of said gas flow channel for fuelgas; an inlet-side through hole and an outlet-side through hole foroxidant gas penetrating the separator which are formed at an inlet-sideend and an outlet-side end of said gas flow channel for oxidant gas; aninlet-side connection groove and an outlet-side connection groove forconnecting said inlet-side and outlet-side through holes for oxidant gaswith said oxidant gas inlet-side manifold aperture and said oxidant gasoutlet-side manifold aperture, respectively, which are formed on saidanode-side; and an inlet-side connection groove and an outlet-sideconnection groove for connecting said inlet-side and outlet-side throughholes for fuel gas with said fuel gas inlet-side manifold aperture andsaid fuel gas outlet-side manifold aperture, respectively, which areformed on said cathode-side.
 10. A conductive separator for a polymerelectrolyte fuel cell, comprising a combination of two separator membersconsisting of an anode-side separator member and a cathode-sideseparator member, each separator member comprising a fuel gas inlet-sidemanifold aperture, a fuel gas outlet-side manifold aperture, an oxidantgas inlet-side manifold aperture, an oxidant gas outlet-side manifoldaperture, a cooling water inlet-side manifold aperture, and a coolingwater outlet-side manifold aperture, said two separator members beingcombined in such a manner that their backsides are in contact with eachother, wherein said anode-side separator member further comprises: a gasflow channel for fuel gas formed on an anode-side of the anode-sideseparator member; an inlet-side through hole and an outlet-side throughhole for fuel gas penetrating the anode-side separator member which areformed at an inlet-side end and an outlet-side end of said gas flowchannel for fuel gas; and an inlet-side connection groove and anoutlet-side connection groove for connecting said inlet-side andoutlet-side through holes for fuel gas with said fuel gas inlet-sidemanifold aperture and said fuel gas outlet-side manifold aperture,respectively, which are formed on the backside of the anode-sideseparator member, said cathode-side separator member further comprises:a gas flow channel for oxidant gas formed on a cathode-side of thecathode-side separator member; an inlet-side through hole and anoutlet-side through hole for oxidant gas penetrating the cathode-sideseparator member which are formed at an inlet-side end and anoutlet-side end of said gas flow channel for oxidant gas; and aninlet-side connection groove and an outlet-side connection groove forconnecting said inlet-side and outlet-side through holes for oxidant gaswith said oxidant gas inlet-side manifold aperture and said oxidant gasoutlet-side manifold aperture, respectively, which are formed on thebackside of the cathode-side separator member, and at least one of saidtwo separator members has, on the backside thereof, a cooling water flowchannel communicating with said cooling water inlet-side manifoldaperture and said cooling water outlet-side manifold aperture such thatthe cooling water flow channel is formed between said two separatormembers.
 11. A conductive separator for a polymer electrolyte fuel cell,comprising a combination of two separator members consisting of ananode-side separator member and a cathode-side separator member, eachseparator member comprising a fuel gas inlet-side manifold aperture, afuel gas outlet-side manifold aperture, an oxidant gas inlet-sidemanifold aperture, an oxidant gas outlet-side manifold aperture, acooling water inlet-side manifold aperture, and a cooling wateroutlet-side manifold aperture, said two separator members being combinedin such a manner that their backsides are in contact with each other,wherein said anode-side separator member further comprises: a gas flowchannel for fuel gas formed on an anode-side of the anode-side separatormember; and an inlet-side through hole and an outlet-side through holefor fuel gas penetrating the anode-side separator member which areformed at an inlet-side end and an outlet-side end of said gas flowchannel for fuel gas, said cathode-side separator member furthercomprises: a gas flow channel for oxidant gas formed on a cathode-sideof the cathode-side separator member; and an inlet-side through hole andan outlet-side through hole for oxidant gas penetrating the cathode-sideseparator member which are formed at an inlet-side end and anoutlet-side end of said gas flow channel for oxidant gas, saidanode-side separator member further comprises: an inlet-side throughhole and an outlet-side through hole for oxidant gas communicating withsaid inlet-side and outlet-side through holes for oxidant gas of saidcathode-side separator member; and an inlet-side connection groove andan outlet-side connection groove for connecting said inlet-side andoutlet-side through holes for oxidant gas of said anode-side separatormember with said oxidant gas inlet-side manifold aperture and saidoxidant gas outlet-side manifold aperture, respectively, which areformed on said anode-side, said cathode-side separator member furthercomprises: an inlet-side through hole and an outlet-side through holefor fuel gas communicating with said inlet-side and outlet-side throughholes for fuel gas of said anode-side separator member; and aninlet-side connection groove and an outlet-side connection groove forconnecting said inlet-side and outlet-side through holes for fuel gas ofsaid cathode-side separator member with said fuel gas inlet-sidemanifold aperture and said fuel gas outlet-side manifold aperture,respectively, which are formed on said cathode-side, and at least one ofsaid two separator members has, on the backside thereof, a cooling waterflow channel communicating with said cooling water inlet-side manifoldaperture and said cooling water outlet-side manifold aperture such thatthe cooling water flow channel is formed between said two separatormembers.